Cooling arrangements using eutectic solutions



- 2,769,310 1956 1 F. s. STICKLAND COOLING ARRANGEMENTS USING EUTECTIC SOLUTIONS Filed Oct. 14, 1952 United States Patent COOLING ARRANGEMENTS USING EUTECTIC SOLUTIONS Frank Samuel Stickland, Orpington, England, assignor to J. Stone & Company (Deptiord) Limited, Deptford, London, England Application October 14, 1952, Serial No. 314,723

Claims priority, application Great Britain October 18, 1951 1 Claim. (Cl. 622) This invention concerns improvements relating to cooling arrangements of the kind comprising a tank containing a eutectic solution serving as a cold retaining medium and provided with a cooling coil by which the said medium can be cooled. The eutectic solution serving only as a cold-retaining medium, affords a store of cold which is available when the cooling coil is out of operation. It is characteristic of arrangements of this kind (hereinafter referred to as the kind set forth) that the cold-retaining eutectic solution is both cooled and gives up its store of cold in the tank itself. Thus, as far as the cooling process is concerned, no circulation of the eutectic solution is called for. Such arrangements, commonly used for cooling vehicles during journeys, are described, for example, in the specification of United States patent application Serial No. 109,865, now Patent No. 2,642,480.

It has been found that when, say, a eutectic solution of sodium chloride contained in a static steel tank is subjected to repeated cycles of freezing and unfreezing, the cold retention or cold holdover gradually falls off from the value which should theoretically be obtained having regard to the latent heat of liquefaction. Thus, with a freshly produced solution, it is possible to obtain a holdover value closely approaching the estimated figure of 104 B. t. u.s/lb. for a solution of sodium chloride having a eutectic temperature of 6 F. After twenty cycles of freezing and unfreezing, however, the

holdover value drops to about 25% of the value for the fresh solution. This loss is ascribed to a change of condition in the solution of which visual evidence is afforded by the deposition of salt crystals in the bottom of the tank. A similar phenomenon has been noted with potassium chromate. The invention seeks to overcome this ditficulty and to insure that a holdover value at least approaching the theoretical figure is maintained.

With this object, according to the invention, an arrangement of the kind set forth comprises in combination with the tank containing the eutectic solution and the coil for cooling the said solution, a pump for positively circulating the solution in the tank. The pump may be a small rotary pump driven by an electric motor and thermostatically controlled so that circulation is produced as long as the solution is at temperatures above or well above its freezing point, for example about 40 F. in the case of sodium chloride. Separation appears to occur only during thawing and circulation during this stage would be sufficient.

One manner of carrying the invention into elfect will now be more fully described by way of example and with reference to the accompanying drawing, in which:

Fig. 1 is a longitudinal section through a tank, on the line II in Fig. 2,

Fig. 2 is a cross section on the line IIII in Fig. 1,

Fig. 3 is a perspective diagram of a bank of such tanks, and

Fig. 4 a circuit diagram.

A fiat plate-shaped steel tank 1 which contains a Patented Nov. 6, 1956 eutectic solution of, say, sodium chloride is provided with a zig-zag tube 2 (Figs. 1 and 3) constituting an evaporator coil which is adapted for being connected to refrigerating apparatus for the periodical pro-cooling of the said solution, the plate itself being thereafter used for cooling purposes, all in well known manner.

For carrying the present invention into effect, the tank 1 or each tank 1 of a bank of tanks (Fig. 3) is provided with an inlet 3 at the top of the tank and an outlet 4 at the bottom. The inlet 3 and outlet 4 of the tank, or of a bank of tanks in series (Fig. 3), are connected to the delivery side 5 and the suction side 6 respectively of a small rotary pump 7, driven by an electric motor 8. The starting and stopping of the motor are controlled by a thermostat 9 whose temperature-sensitive element is located in the suction line 10 of the pump. The thermostat 9 is arranged to control the motor 8 in such a manner that the pump 7 is driven and the solution positively maintained in circulation as long as the temperature of the solution is well above its freezing point, for example about 40 F. in the case of sodium chloride. As will be understood, the solution is drawn off at the bottom of the tank or tanks and is delivered to the top of the said tank or tanks, so that the whole of the solution is subject to the agitating effect of the circulation. If desired, the inlet 3 and outlet 4 may be disposed near diagonally opposite corners of the tank.

Several tanks 1 may be connected in series to a single pump 7, the outlet 4 of one tank being connected to the inlet 3 of the next, as shown in Fig. 3. As, especially in such a case, the sealing of each tank 1 under vacuum would present difliculty, each tank is vented to the air through a plug 11 (Figs. 1 and 2). As the tanks 1 cannot be completely filled, because room must be left for expansion of the solution on freezing, only tanks at the same level can be connected to a common pump 7. Tanks or banks of tanks at different levels should be connected to individual pumps.

As illustrated in Fig. 4, a thermostat of the known mercury-in-glass type is connected in series with the winding 12 of a thermostat relay when contacts 13 are in turn connected in series with the winding 14 of a main relay. The contacts 15 of the latter relay control the supply of current to the motor 8 from D. C. supply mains 16. Also connected in series with the thermostat 9 and 1 winding 12 are contacts 17 of a master control switch and interlock contacts 18 which are closed only when the current supply (usually A. C.) is connected to the refrigerating apparatus for pre-cooling. Consequently, the motor 8 is energized to drive the circulating pump 7 only as long as the temperature in the line 10 is above the predetermined value for the thermostat 9 and then only if the control switch contacts 17 and the interlock contacts 18 have been closed.

I claim:

In refrigerating arrangements, a tank for containing a eutectic solution serving as a cold-storing medium, said tank having walls through which heat passes by conduction to the eutectic solution for effecting the cooling, a cooling coil extending within said tank for flow of a fluid refrigerating medium for cooling and freezing said eutectic solution, means for withdrawing said eutectic solution from said tank when in the liquid state and agitating said withdrawn solution to reduce precipitation and settling out of the solute of said eutectic solution, said withdrawing and agitating means comprising a system of piping connected with said tank, a pump connected in said system, an electric motor connected for driving said pump, said motor having an electric current supply circuit connected thereto, a current connecting and interrupting device connected in said circuit, thermostatic means responsive solely to the temperature of the eutectic solution for controlling said current connecting and interrupting device to close said circuit and supply current to said motor only when said solution is at a temperature substantially above its freezing point.

References Cited in the file of this patent UNITED STATES PATENTS 2,117,505 Reinhardt May 17, 1938 4 Huber Aug. 11, 1942 Morrison Aug. 31, 1948 Kleist Jan. 16, 1951 

